1. Field of the Invention
The present invention relates to an ink jet printer. The present invention further relates to a method of discharging ink from the ink jet printer.
2. Description of the Related Art
Ink jet printers are widely known. Ink jet printer generally comprises an ink chamber, a pressure chamber, a nozzle, an actuator and a controller. The ink chamber stores ink. The pressure amber is connected with the ink chamber. The nozzle is connected with the pressure chamber. The actuator generally has a piezoelectric element. The piezoelectric element is disposed in the vicinity of the pressure chamber. Volume of the pressure chamber changes when the piezoelectric element is deformed due to piezoelectric effects. The controller controls the actuator by changing voltage applied to the piezoelectric element.
The controller changes the voltage applied to the piezoelectric element in order to discharge ink. The controller changes the voltage applied to the piezoelectric element such that the pressure in the pressure chamber is reduced. That is, the controller changes the shape of the piezoelectric element such that the volume of the pressure chamber increases. As a result, the ink moves from the ink chamber to the pressure chamber. Thereupon, the controller changes the voltage applied to the piezoelectric element such that the volume of the pressure chamber is increased. That is, the controller changes the shape of the piezoelectric element such that the volume of the pressure chamber decreases. By this means, pressure is applied to the ink that has been filled within the pressure chamber, and the ink is discharged from the nozzle.
When the time or period between the reduction and the subsequent increase of pressure in the pressure chamber is changed, there is a change in the quantity of ink discharged from the nozzle. Printing density changes when there is a change in the quantity of ink discharged. An important factor in stabilizing printing density is to control the time or period that elapses between the reduction and the subsequent increase of pressure in the pressure chamber.
Japanese Patent Application Publication No. 2003-145750 (U.S. Pat. No. 6,523,923) discloses a technique for determining the time between the reduction and the subsequent increase of pressure in the pressure chamber. In this technique, the period for a pressure wave developed within the ink to propagate from the ink chamber to the nozzle (below, this period will be termed a one-way propagation period) is used as an index, and the time between the reduction and the subsequent increase of pressure in the pressure chamber is determined using this index. If the time between the reduction and the subsequent increase of pressure in the pressure chamber is identical with the one-way propagation period, the actuator can efficiently decrease and increase the pressure of the ink. That is, considerable pressure change can be applied to the ink in the pressure chamber. When pressure change is applied efficiently to the ink, the ink can be discharged efficiently.